This invention relates to a scroll compressor of a differential pressure oil-supply type, and, more particularly to a scroll compressor including means for maintaining a differential pressure oil-supply in a wide operation range.
A scroll compressor of the aforementioned type is proposed in, for example, U.S. Pat. No. 4,365,941 wherein an intermediate pressure chamber on the back of an orbiting scroll.
A pressure of the intermediate pressure chamber is governed by a pressure of an airtight chamber which is communicated with the intermediate pressure chamber through a communication hole and roughly maintained at an average pressure of the airtight chamber. The pressure of the airtight chamber is governed by a suction pressure according to characteristics of the scroll compressor and that value is determined by a position of the communication hole. In other words, the intermediate pressure is detemined by the suction pressure and the communication hole position independent of discharge pressure.
However, in the above-noted scroll compressor, as oil is supplied to the sliding part by a differential pressure between the discharge pressure and the intermediate pressure, if the differential pressure is small or null, the oil cannot be supplied to the sliding part so that the operation is impossible. Also, when the communication hole is provided at the position where the intermediate pressure is low in order to maintain the differential pressure, a force pressing the orbiting scroll against a stationary scroll produced by the intermediate pressure is insufficient when the pressure differential between the suction pressure and the discharge pressure is so great that sealing between tips of lapping parts and flat plate parts becomes impossible.
It is an object of the pressent invention to provide a scroll compressor which facilitates maintaining an oil-supply pressure within a wide operation range.
In a scroll compressor, when suction pressure is constant and discharge pressure is low, the force pressing the orbiting scroll against the stationary scroll can be small compared to when the discharge pressure is high. According to the present invention, a scroll compressor is provided with a valve which can switch connection of an intermediate pressure chamber to a lower intermediate pressure or to a higher intermediate pressure of a compressor part, and is constructed so that when the discharge pressure is below a certain value, the intermediate pressure chamber is connected to the lower intermediate pressure side of the compressor by the valve to maintain oil-supply pressure and, when the discharge pressure is above the certain value, the intermediate pressure chamber is connected to the higher intermediate pressure side of the compressor part by the valve which maintains the oil-supply pressure.